The technology of mobile telecommunication developed substantially since the first generation mobile communication system (1G). Even though 1G showed poor stability, coverage and sound quality the interest in mobile communications was evident. The capacity of 1G was limited by the analogue technology employed. A significant improvement was achieved with the digital technology introduced in 2G. With the introduction of 2G coverage, stability and security capacities increased, while at the same time more users could be served and data services became available. Examples of 2G systems are the Global System for Mobile communications (GSM) and Interim Standard 95 (IS-95) adopted in Europe and in the United States respectively. 2G systems of today are pushed to their limits using techniques like General Packet Radio Service (GPRS), offering higher data rates and thus supporting transmission of low resolution photos and limited multimedia applications.
In order to satisfy the expected needs from future applications like multimedia and video-streaming the third generation mobile communication system (3G) will replace its predecessors. The 3G system used in Europe is called Universal Mobile Telecommunications Services (UMTS). A similar system called CDMA2000 is used in the United States. The air interface used in UMTS is Wideband Code-Division Multiple Access (WCDMA). The first fully commercialized WCDMA service was operational in 2001 and since then an ongoing evolvement has taken place to increase resource utilization. WCDMA Release 5 introduced the high-speed downlink packet access (HSDP A) to improve downlink capacity, i.e. the capacity of transmission from the base transceiver station (NodeB) to the user equipment (UE). HSDPA forms part of a collection of High-Speed Packet Access (HSP A) protocols for mobile telephony that extend and improve the performance of existing UMTS protocols. Within HSP A further a high-speed uplink packet access (HSUP A) protocol is developed for an improved uplink communication, i.e. for improving the capacity of transmission from the user equipment to the NodeB.
HSUPA provides improved up-link performance of up to up to 5.76 Mbits/s theoretically. HSUPA is expected to use an uplink enhanced dedicated channel (E-DCH) on which it will employ link adaptation methods similar to those employed by HSDPA, namely a shorter Transmission Time Interval and HARQ (hybrid ARQ) with incremental redundancy.
The shorter Transmission Time Interval enables a faster matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link (e.g. the pathloss, the interference due signals coming from other transmitters, the sensitivity of the receiver, the available transmitter power margin, etc.).
HARQ (hybrid automatic repeat request) with incremental redundancy results in more effective retransmissions.
Similarly to HSDPA, HSUPA uses a packet scheduler, but it operates on a request-grant principle where the UEs request a permission to send data and the scheduler decides when and how many UEs will be allowed to do so. A request for transmission contains data about the state of the transmission buffer and the queue at the UE and its available power margin.
In addition to this scheduled mode of transmission the standards also allows a self-initiated transmission mode from the UEs, denoted non-scheduled. The non-scheduled mode can, for example, be used for VoIP services for which even the reduced TTI and the Node-B based scheduler will not be able to provide the very short delay time and constant bandwidth required.
Each MAC-d flow (i.e. QoS flow) is configured to use either scheduled or non-scheduled modes; the UE adjusts the data rate for scheduled and non-scheduled flows independently. The maximum data rate of each non-scheduled flow is configured at call setup, and typically not changed frequently. The power used by the scheduled flows is controlled dynamically by the Node-B through absolute grant (consisting of an actual value) and relative grant (consisting of a single up/down bit) messages.
The transport channel structure proposed for HSUPA comprises the following channels:
E-DPDCH, E-AGCH, E-RICH and E-DPCCH.
E-DPDCH is the Enhanced Dedicated Physical Data CHannel. This is the physical channel on radio interface (Uu) dedicated to a particular user on which payload (e.g. IP data, voice) as well as higher layer signalling (RRC and Non Access Stratum [NAS] signalling) is transmitted on the uplink by the UE (user equipment) to the Node-B.
E-AGCH: E-DCH Absolute Grant Channel (E-AGCH) is a fixed rate downlink physical channel carrying the uplink E-DCH absolute grant (power allocation). An E-DCH absolute grant shall be transmitted over one E-AGCH sub-frame or one E-AGCH frame.
The following information is transmitted by means of the absolute grant channel (E-AGCH):                Absolute Grant Value: 5 bits        Absolute Grant Scope: 1 bit        
E-HICH or E-DCH HARQ Acknowledgement Indicator Channel is a downlink physical channel that carries ACK/NACK indications for TDD enhanced uplink. The ACK/NACK command is mapped to the HARQ acknowledgement indicator with 2 bits.
DPCCH, Dedicated Physical Control CHannel, is the physical channel from layer 2 on which the signaling is transmitted on the uplink by the UE to the Node-B.
The following information is transmitted by means of the E-DPCCH:                Retransmission sequence number (RSN): 2 bits        E-TFCI (Transport Format Combination Indicator): 7 bits        “Happy” bit:        
Document 3GPP TS 25.212: “Multiplexing and channel coding (FDD)” proposes a TD-SCDMA system for use in the 3GPP standard. According to this proposal, the length of one radio frame is 10 ms and each frame is divided into 2 equal sub-frames of 5 ms. As shown in FIG. 1, a sub-frame constitutes of two kinds of Time Slot (TS): normal TS (TS0˜TS6) and special TS (GP, DwPTS, UpPTS), where TS0 and TS1 are always designated as downlink and uplink TS respectively, DwPTS and UpPTS are the dedicated downlink and uplink pilot TSs used for downlink and uplink synchronization respectively, and GP is a guard period. The guard period GP is used to avoid interference between uplink and downlink transmissions, as well as to absorb the propagation delays between the Mobile Station and the base station when the first one sends the first signal on the UpPTS channel; at this stage in fact the propagation delay is not yet known. The switching point defines the transition from uplink to downlink. By way of example FIG. 1 shows a switching point between time slots TS3 and TS4.
According to the number of spreading codes, TSi (i=0,1, . . . 6) is divided into several code channels (e.g. 4, 8, 16, etc.), which are used to transmit traffic data and some control signals.
FIG. 1 shows an example of the TD-SCDMA frame structure and physical layer configuration, in the case of 16 code channels (spreading factor=16).
The duration of the different useful time slots is expressed through a measurement unit called chip, of the duration of 0,78125 μs, equal to the reciprocal of a chiprate =1,28 Mcps corresponding to the common frequency of a set of N sequences of codes used in a useful time slot to perform the spread spectrum according to the CDMA technique.
In document 3GPP TSG RAN WG1 #46 Tdoc R1-062331: LCR TDD: Structure and Coding for E-AGCH and E-HICH, a multiplexed E-HICH structure carrying multiple ACK/NACKs towards multiple end users for TD-SCDMA is proposed on a double spreading scheme.
There are at most 5 timeslots used for uplink (from TS1 to TS5) in a TTI (sub-frame), giving a total number of 80 RUs per TTI (sub-frame). We number the resource units (RUs) in terms of timeslot and code. Timeslot 1 carries resource units 0,1, 2, . . . , 15, timeslot 2 carries resource units 16,17, . . . , 31, and so on, as illustrated in FIG. 3.
Channel coding process for E-HICH is proposed below as shown schematically in FIG. 17:
Each ACK/NACK indicator is firstly spread by the corresponding signature sequence (in this case a sequence of 80 bits). The signature sequence is also known and as spreading sequence or signature waveform). To be able to perform the despreading operation, the receiver must not only know the code sequence used to spread the signal, but the code of the received signal and the locally generated code must also be synchronised. The signature sequence identifies the user. Multiple signature sequences may be assigned to the same user, e.g. for a signature sequence for acknowledge messages, a signature sequence for power assignments and/or synchronization. This process is described in detail in 3GPP TSG RAN WG1#46, Tdoc R1-062331 Spare bits may be appended to the resulting sequence to add further information.
Bit scrambling is applied to each of the 88-bit sequence. In addition to spreading, part of the process on the transmitter is the scrambling operation. This is needed to separate terminals or base stations from each other. Scrambling is used on top of spreading, so it does not change the signal bandwidth but only makes the signals from different sources separable from each other. With the scrambling it would not matter if the actual spreading were done with identical code for several transmitters. The scrambling codes at the uplink separate the terminals and at the downlink separate the sectors.
Subsequent to the step of scrambling the signal may be interleaved, to minimize the consequences of burst errors. The interleaving scheme can either be block or convolutional interleaving.
Each Sequence after bit scrambling is QPSK modulated and amplitude-weighted.
Multiple acknowledgement indicators are multiplexed. (Multiplexing is transparent when only one ACK/NACK indicator is carried on the E-HICH.)
Physical channel spreading and scrambling operation are then performed in the usual manner
3GPP TSG RAN WG1#46, Tdoc R1-062331 shows that in a Pedestrian-B channel, a 1% ACK/NACK error probability is achieved at an E-HICH Ec/Ioc of −5.5 dB with default allocation scheme and −10 dB with common allocation scheme. For a typical deployment, the 5% point of the geometry CDF is assumed at an Îor/Ioc of approximately −5 dB, this indicates that: in one timeslot per frame at the stated reliability, an E-HICH acknowledgement would occupy at-most 22.3% of Node-B power with default allocation scheme. Using common midamble allocation mode this could be reduced to 7.9% per user.
Nevertheless, since multiple ACK/NACKs share one OVSF code, i.e. one midamble, further enhanced techniques, such as beamforming on E-HICH to achieve even lower power consumption are not applicable. Moreover, considering the future long term evolution (LTE) system, much more RUs are employed due to the broad band transmission. The existing “one-to-one” schemes need longer signature sequence for mapping the RUs, which will reduce the transmission efficiency.